U.S. patent number 8,273,216 [Application Number 11/642,390] was granted by the patent office on 2012-09-25 for process for the production of paper.
This patent grant is currently assigned to Akzo Nobel N.V.. Invention is credited to Joakim Carlen, Birgitta Johansson, Fredrik Solhage.
United States Patent |
8,273,216 |
Solhage , et al. |
September 25, 2012 |
Process for the production of paper
Abstract
The present invention relates to a process for producing paper
which comprises: providing an aqueous suspension comprising
cellulosic fibers, adding to the suspension, after all points of
high shear, a cationic polysaccharide; and a polymer P2 being an
anionic polymer; and, dewatering the obtained suspension to form
paper.
Inventors: |
Solhage; Fredrik (Bor{dot over
(a)}s, SE), Carlen; Joakim (Goteborg, SE),
Johansson; Birgitta (Nodinge, SE) |
Assignee: |
Akzo Nobel N.V. (Arnhem,
NL)
|
Family
ID: |
38223153 |
Appl.
No.: |
11/642,390 |
Filed: |
December 20, 2006 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20070151688 A1 |
Jul 5, 2007 |
|
Related U.S. Patent Documents
|
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
|
60755350 |
Dec 30, 2005 |
|
|
|
|
Current U.S.
Class: |
162/168.3;
162/175; 162/181.6; 162/164.1; 162/158; 162/185; 162/164.6 |
Current CPC
Class: |
D21H
23/18 (20130101); D21H 21/10 (20130101); D21H
17/74 (20130101); D21H 17/43 (20130101); D21H
17/455 (20130101); D21H 17/66 (20130101); D21H
17/29 (20130101); D21H 17/68 (20130101); D21H
17/375 (20130101) |
Current International
Class: |
D21H
17/29 (20060101); D21H 17/45 (20060101); D21H
17/63 (20060101); D21H 21/10 (20060101) |
Field of
Search: |
;162/158,164.1,164.6,168.3,175,181.6,185 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
0 234 513 |
|
Sep 1987 |
|
EP |
|
0 234 513 |
|
Sep 1987 |
|
EP |
|
0 490 425 |
|
Jun 1992 |
|
EP |
|
0 522 940 |
|
Jan 1993 |
|
EP |
|
1 039 026 |
|
Sep 2000 |
|
EP |
|
1 238 161 |
|
May 2001 |
|
EP |
|
01-162897 |
|
Jun 1989 |
|
JP |
|
2002-513102 |
|
May 2002 |
|
JP |
|
2005-195486 |
|
Jul 2005 |
|
JP |
|
2006-501348 |
|
Jan 2006 |
|
JP |
|
2009-503034 |
|
Jan 2009 |
|
JP |
|
200400305 |
|
Jan 2004 |
|
TW |
|
200426275 |
|
Dec 2004 |
|
TW |
|
WO 91/07543 |
|
May 1991 |
|
WO |
|
WO 95/33097 |
|
Dec 1995 |
|
WO |
|
WO 97/04168 |
|
Feb 1997 |
|
WO |
|
WO 99/14432 |
|
Mar 1999 |
|
WO |
|
WO 99/55962 |
|
Nov 1999 |
|
WO |
|
WO 00/11267 |
|
Mar 2000 |
|
WO |
|
WO 01/34910 |
|
May 2001 |
|
WO |
|
WO 01/34910 |
|
May 2001 |
|
WO |
|
WO 02/33171 |
|
Apr 2002 |
|
WO |
|
WO 03/064767 |
|
Aug 2003 |
|
WO |
|
WO 2004/015200 |
|
Feb 2004 |
|
WO |
|
WO 2004/015200 |
|
Feb 2004 |
|
WO |
|
WO 2004/031478 |
|
Apr 2004 |
|
WO |
|
WO 2004/104299 |
|
Dec 2004 |
|
WO |
|
WO 2005/116336 |
|
Aug 2005 |
|
WO |
|
Other References
Wurzburg, "Modified Starches: Properties and Uses", CRC Press, Boca
Raton, FL, 2000, pp. 113-116. cited by examiner .
Greenberg, S.A. "The Chemistry of Silicic Acid" Journal of Chemical
Education, vol. 36, No. 5, 1959, pp. 218-219. cited by examiner
.
Japanese Office Action for Japanese Application No. 2007-548139
dated Feb. 9, 2010. cited by other .
English Language Translation of the Japanese Office Action for
Japanese Application No. 2007-548139 dated Feb. 9, 2010. cited by
other .
Taiwanese Examination Report for Taiwan Patent Application No.
95148730. cited by other .
English language translation of Taiwanese Examination Report for
Taiwan Patent Application No. 95148730. cited by other .
USPTO Non-Final Office Action dated Mar. 27, 2008 relating to case
U.S. Appl. No. 11/302,941 filed Dec. 14, 2005. cited by other .
USPTO Final Office Action dated Dec. 31, 2008 relating to case U.S.
Appl. No. 11/302,941 filed Dec. 14, 2005. cited by other .
USPTO Non-Final Office Action dated May 4, 2009 relating to case
U.S. Appl. No. 11/302,941 filed Dec. 14, 2005. cited by other .
USPTO Final Office Action dated Feb. 3, 2010 relating to case U.S.
Appl. No. 11/302,941 filed Dec. 14, 2005 . cited by other .
English translation of WO 2005/116336 A1. Date: 2006. cited by
other .
"Bentonite", product information sheet, Arokor Holdings, Inc.
[online] [retrieved from the Internet on Dec. 28, 2008]. cited by
other .
Falcone, J. "Silicon Compounds: Anthropogenic Silicas and
Silicates," Kirk-Othmer Encyclopedia of Chemical Tehnology, 2001,
by John Wiley & Sons, Inc., pp. 1-6. cited by other .
Sears, Jr., G. W., "Determination of Specific Surface Area of
Colloidal Silica by Titration with Sodium Hydroxide," Analytical
Chem., vol. 28, No. 12 (1956), pp. 1981-1983. cited by other .
Iler, Ralph K. et al., "Degree of Hydration of Particles of
Colloidal Silica in Aqueous Solution," J. Phys. Chem., vol. 60
(1956) pp. 955-957. cited by other .
Japanese Office Action for JP 2008-548467 dated Jul. 5, 2011. cited
by other .
English translation of Japanese Office Action for JP 2008-548467
dated Jul. 5, 2011. cited by other .
Japanese Office Action for JP 2008-548467 dated Jan. 17, 2012.
cited by other .
English translation of Japanese Office Action for JP 2008-548467
dated Jan. 17, 2012. cited by other .
English lanugage abstract for JP 2005-195486, Jul. 21, 2005. cited
by other.
|
Primary Examiner: Daniels; Matthew
Assistant Examiner: Cordray; Dennis
Attorney, Agent or Firm: Morriss; Robert C.
Claims
The invention claimed is:
1. A process for producing paper which comprises: (i) providing an
aqueous suspension comprising cellulosic fibers, (ii) adding to the
suspension after all points of high shear: a polymer P1 being a
water-soluble cationic acrylamide-based polymer having an average
molecular weight of at least about 1,000,000 prepared by
polymerizing a composition comprising a monomer mixture comprising
one or more cationic monomers represented by the general structural
formula (II) ##STR00003## wherein R.sub.1 is H or CH.sub.3; R.sub.2
and R.sub.3 are each H or a hydrocarbon group having from 1 to 2
carbon atoms; A is O; B is an alkyl or alkylene group having from 2
to 8 carbon atoms; R.sub.4 is H or a hydrocarbon group having from
1 to 2 carbon atoms; and X.sup.- is an anionic counterion; a
cationic starch having a degree of cationic substitution (DS.sub.C)
from 0.01 to 0.5, a charge density of from about 0.05 to about 6.0
meq/g and a weight average molecular weight of above about
1,000,000; and a polymer P2 being an anionic polymer selected from
anionic silica-based polymers comprising anionic silica-based
particles having an average particle size in the range of from
about 1 to about 10 nm, and a specific surface area within the
range of from 50 to 1000 m.sup.2/g; and (iii) dewatering the
obtained suspension to form paper.
2. The process according to claim 1, wherein the cationic starch
has a degree of cationic substitution (DS.sub.C) within the range
of from about 0.025 to about 0.2.
3. The process according to claim 1, wherein the cationic starch
has a cationic charge density within the range of from about 0.1 to
about 5.0 meq/g.
4. The process according to claim 1, wherein the anionic
silica-based polymers are prepared by condensation polymerization
of siliceous compounds.
5. The process according to claim 1, wherein the one or more
cationic monomers are chosen from dimethylammoniumethyl acrylate
methyl chloride, dimethylammoniumethyl methacrylate methyl
chloride, diethylammoniumethyl acrylate methyl chloride,
diethylammoniumethyl methacrylate methyl chloride, or mixtures
thereof.
6. The process according to claim 1, wherein the one or more
cationic monomers are chosen from dimethylaminoethyl acrylate
methyl chloride quaternary salt, and dimethylaminoethyl
methacrylate methyl chloride quaternary salt, or mixtures
thereof.
7. A process for producing paper which comprises: (i) providing an
aqueous suspension comprising cellulosic fibers, (ii) adding to the
suspension after all points of high shear: a polymer P1 being a
water-soluble cationic acrylamide-based polymer having an average
molecular weight of at least about 1,000,000 prepared by
polymerizing a composition comprising a monomer mixture comprising
one or more cationic monomers represented by the general structural
formula (II) ##STR00004## wherein R.sub.1 is H or CH.sub.3, R.sub.2
and R.sub.3 are each H or a hydrocarbon group having from 1 to 2
carbon atoms; A is O; B is an alkyl or alkylene group having from 2
to 8 carbon atoms; R.sub.4 is H or a hydrocarbon group having from
1 to 2 carbon atoms; and X.sup.- is an anionic counterion; a
cationic polysaccharide having a degree of substitution (DSc)
within the range of from about 0.01 to about 0.5 and a weight
average molecular weight of above about 1,000,000; and a polymer P2
being an anionic polymer selected from anionic silica-based
polymers comprising anionic silica-based particles having an
average particle size in the range of from about 1 to about 10 nm,
and a specific surface area within the range of from 50 to 1000
m.sup.2/g; said points of high shear comprising pumping and
cleaning stages; the obtained suspension from step (ii) being fed
to a headbox which ejects the suspension comprising polymer P1,
cationic starch, and polymer P2 onto a forming wire for drainage to
form paper, wherein the stages of pumping and cleaning comprise fan
pumps, pressure screens and centri-screens.
8. The process according to claim 7, wherein the last point of high
shear occurs at a centri-screen.
9. The process according to claim 7, wherein the cationic
polysaccharide is cationic starch.
10. The process according to claim 7, wherein the cationic
polysaccharide has a degree of substitution (DS.sub.C) within the
range of from about 0.02 to about 0.3.
11. The process according to claim 7, wherein the cationic
polysaccharide has a cationic charge density within the range of
from about 0.05 to about 6.0 meq/g.
12. The process according to claim 7, wherein the anionic
silica-based polymers are prepared by condensation polymerization
of siliceous compounds.
13. The process according to claim 7, wherein the one or more
cationic monomers are chosen from dimethylammoniumethyl acrylate
methyl chloride, dimethylammoniumethyl methacrylate methyl
chloride, diethylammoniumethyl acrylate methyl chloride,
diethylammoniumethyl methacrylate methyl chloride, or mixtures
thereof.
14. The process according to claim 7, wherein the one or more
cationic monomers are chosen from dimethylaminoethyl acrylate
methyl chloride quaternary salt, and dimethylaminoethyl
methacrylate methyl chloride quaternary salt, or mixtures thereof.
Description
The present invention relates to a process for the production of
paper. More specifically, the invention relates to a process for
the production of paper which comprises adding cationic starch and
a polymer P2 to an aqueous cellulosic suspension after all points
of high shear and dewatering the obtained suspension to form
paper.
BACKGROUND
In the art of papermaking, an aqueous suspension containing
cellulosic fibres, and optional fillers and additives, referred to
as stock, is fed through pumps, screens and cleaners, which subject
the stock to high shear forces, into a headbox which ejects the
stock onto a forming wire. Water is drained from the stock through
the forming wire so that a wet web of paper is formed on the wire,
and the web is further dewatered and dried in the drying section of
the paper machine. Drainage and retention aids are conventionally
introduced at different points in the flow of stock in order to
facilitate drainage and increase adsorption of fine particles such
as fine fibres, fillers and additives onto the cellulose fibres so
that they are retained with the fibres on the wire. Examples of
conventionally used drainage and retention aids include organic
polymers, inorganic materials, and combinations thereof.
EP 0 234513 A1, WO 91/07543 A1, WO 95/33097 A1 and WO 01/34910 A1
disclose the use of cationic starch and an anionic polymer in
paper-making processes. However, there is nothing disclosed about
adding both these components to the suspension after all points of
high shear.
It would be advantageous to be able to provide a papermaking
process with further improvements in drainage, retention and
formation.
THE INVENTION
According to the present invention it has been found that drainage
can be improved without any significant impairment of retention and
paper formation, or even with improvements in retention and paper
formation, by a process for producing paper which comprises: (i)
providing an aqueous suspension comprising cellulosic fibres, (ii)
adding to the suspension after all points of high shear: a cationic
polysaccharide and a polymer P2 being an anionic polymer; and,
(iii) dewatering the obtained suspension to form paper. The present
invention provides improvements in drainage and retention in the
production of paper from all types of stocks, in particular stocks
containing mechanical or recycled pulp, and stocks having high
contents of salts (high conductivity) and colloidal substances, and
in papermaking processes with a high degree of white water closure,
i.e. extensive white water recycling and limited fresh water
supply. Hereby the present invention makes it possible to increase
the speed of the paper machine and to use lower dosages of polymers
to give corresponding drainage and/or retention effects, thereby
leading to an improved papermaking process and economic
benefits.
The term "drainage and retention aids", as used herein, refers to
two or more components which, when added to an aqueous cellulosic
suspension, give better drainage and retention than is obtained
when not adding the said two or more components.
The cationic polysaccharide according to this invention can be
selected from any polysaccharide known in the art including, for
example, starches, guar gums, celluloses, chitins, chitosans,
glycans, galactans, glucans, xanthan gums, pectins, mannans,
dextrins, preferably starches and guar gums. Examples of suitable
starches include potato, corn, wheat, tapioca, rice, waxy maize,
barley etc. Suitably the cationic polysaccharide is
water-dispersable or, preferably, water-soluble.
Particularly suitable polysaccharides according to the invention
include those comprising the general structural formula (I):
##STR00001## wherein P is a residue of a polysaccharide; A is a
group attaching N to the polysaccharide residue, suitably a chain
of atoms comprising C and H atoms, and optionally O and/or N atoms,
usually an alkylene group with from 2 to 18 and suitably 2 to 8
carbon atoms, optionally interrupted or substituted by one or more
heteroatoms, e.g. O or N, e.g. an alkyleneoxy group or hydroxy
propylene group (--CH.sub.2--CH(OH)--CH.sub.2--); R.sub.1, R.sub.2,
and R.sub.3 are each H or, preferably, a hydrocarbon group,
suitably alkyl, having from 1 to 3 carbon atoms, suitably 1 or 2
carbon atoms; n is an integer from about 2 to about 300,000,
suitably from 5 to 200,000 and preferably from 6 to 125,000 or,
alternatively, R.sub.1, R.sub.2 and R.sub.3 together with N form a
aromatic group containing from 5 to 12 carbon atoms; and X.sup.- is
an anionic counterion, usually a halide like chloride.
Cationic polysaccharides according to the invention may also
contain anionic groups, preferably in a minor amount. Such anionic
groups may be introduced in the polysaccharide by means of chemical
treatment or be present in the native polysaccharide.
The weight average molecular weight of the cationic polysaccharide
an vary within wide limits dependent on, inter alia, the type of
polymer used, and usually it is at least about 5,000 and often at
least 10,000. More often, it is above 150,000, normally above
500,000, suitably above about 700,000, preferably above about
1,000,000 and most preferably above about 2,000,000. The upper
limit is not critical; it can be about 200,000,000, usually
150,000,000 and suitably 100,000,000.
The cationic polysaccharide can have a degree of cationic
substitution (DS.sub.C) varying over a wide range dependent on,
inter alia, the type of polymer used; DS.sub.C can be from 0.005 to
1.0, usually from 0.01 to 0.5, suitably from 0.02 to 0.3,
preferably from 0.025 to 0.2.
Usually the charge density of the cationic polysaccharide is within
the range of from 0.05 to 6.0 meq/g of dry polymer, suitably from
0.1 to 5.0 and preferably from 0.2 to 4.0.
The polymer P2 according to the present invention is an anionic
polymer which can be selected from inorganic and organic anionic
polymers. Examples of suitable polymers P2 include water-soluble
and water-dispersible inorganic and organic anionic polymers.
Examples of suitable polymers P2 include inorganic anionic polymers
based on silicic acid and silicate, i.e., anionic silica-based
polymers. Suitable anionic silica-based polymers can be prepared by
condensation polymerisation of siliceous compounds, e.g. silicic
acids and silicates, which can be homopolymerised or
co-polymerised. Preferably, the anionic silica-based polymers
comprise anionic silica-based particles that are in the colloidal
range of particle size. Anionic silica-based particles are usually
supplied in the form of aqueous colloidal dispersions, so-called
sols. The silica-based sols can be modified and contain other
elements, e.g. aluminium, boron, nitrogen, zirconium, gallium and
titanium, which can be present in the aqueous phase and/or in the
silica-based particles. Examples of suitable anionic silica-based
particles include polysilicic acids, polysilicic acid microgels,
polysilicates, polysilicate microgels, colloidal silica, colloidal
aluminium-modified silica, polyaluminosilicates,
polyaluminosilicate microgels, polyborosilicates, etc. Examples of
suitable anionic silica-based particles include those disclosed in
U.S. Pat. Nos. 4,388,150; 4,927,498; 4,954,220; 4,961,825;
4,980,025; 5,127,994; 5,176,891; 5,368,833; 5,447,604; 5,470,435;
5,543,014; 5,571,494; 5,573,674; 5,584,966; 5,603,805; 5,688,482;
and 5,707,493; which are hereby incorporated herein by
reference.
Examples of suitable anionic silica-based particles include those
having an average particle size below about 100 nm, preferably
below about 20 nm and more preferably in the range of from about 1
to about 10 nm. As conventional in the silica chemistry, the
particle size refers to the average size of the primary particles,
which may be aggregated or non-aggregated. Preferably, the anionic
silica-based polymer comprises aggregated anionic silica-based
particles. The specific surface area of the silica-based particles
is suitably at least 50 m.sup.2/g and preferably at least 100
m.sup.2/g. Generally, the specific surface area can be up to about
1700 m.sup.2/g and preferably up to 1000 m.sup.2/g. The specific
surface area is measured by means of titration with NaOH as
described by G. W. Sears in Analytical Chemistry 28(1956): 12,
1981-1983 and in U.S. Pat. No. 5,176,891 after appropriate removal
of or adjustment for any compounds present in the sample that may
disturb the titration like aluminium and boron species. The given
area thus represents the average specific surface area of the
particles.
In a preferred embodiment of the invention, the anionic
silica-based particles have a specific surface area within the
range of from 50 to 1000 m.sup.2/g, more preferably from 100 to 950
m.sup.2/g. Preferably, the silica-based particles are present in a
sol having a S-value in the range of from 8 to 50%, preferably from
10 to 40%, containing silica-based particles with a specific
surface area in the range of from 300 to 1000 m.sup.2/g, suitably
from 500 to 950 m.sup.2/g, and preferably from 750 to 950
m.sup.2/g, which sols can be modified as mentioned above. The
S-value is measured and calculated as described by Iler &
Dalton in J. Phys. Chem. 60(1956), 955-957. The S-value indicates
the degree of aggregation or microgel formation and a lower S-value
is indicative of a higher degree of aggregation.
In yet another preferred embodiment of the invention, the
silica-based particles have a high specific surface area, suitably
above about 1000 m.sup.2/g. The specific surface area can be in the
range of from 1000 to 1700 m.sup.2/g and preferably from 1050 to
1600 m.sup.2/g.
Further examples of suitable polymers P2 include water-soluble and
water-dispersible organic anionic polymers obtained by polymerizing
an ethylenically unsaturated anionic or potentially anionic monomer
or, preferably, a monomer mixture comprising one or more
ethylenically unsaturated anionic or potentially anionic monomers,
and optionally one or more other ethylenically unsaturated
monomers. Preferably, the ethylenically unsaturated monomers are
water-soluble. Examples of suitable anionic and potentially anionic
monomers include ethylenically unsaturated carboxylic acids and
salts thereof, ethylenically unsaturated sulphonic acids and salts
thereof, e.g. any one of those mentioned above. The monomer mixture
can contain one or more water-soluble ethylenically unsaturated
non-ionic monomers. Examples of suitable copolymerizable non-ionic
monomers include acrylamide and the above-mentioned non-ionic
acrylamide-based and acrylate-based monomers and vinylamines. The
monomer mixture can also contain one or more water-soluble
ethylenically unsaturated cationic and potentially cationic
monomers, preferably in minor amounts. Examples of suitable
copolymerizable cationic monomers include the monomers represented
by the above general structural formula (I) and diallyldialkyl
ammonium halides, e.g. diallyldimethyl ammonium chloride. The
monomer mixture can also contain one or more polyfunctional
crosslinking agents. The presence of a polyfunctional crosslinking
agent in the monomer mixture renders possible preparation of
polymers P2 that are water-dispersible. Examples of suitable
polyfunctional crosslinking agents including the above-mentioned
polyfunctional crosslinking agents. These agents can be used in the
above-mentioned amounts. Examples of suitable water-dispersible
organic anionic polymers include those disclosed in U.S. Pat. No.
5,167,766, which is incorporated herein by reference. Examples of
preferred copolymerizable monomers include (meth)acrylamide, and
examples of preferred polymers P2 include water-soluble and
water-dispersible anionic acrylamide-based polymers.
The polymer P2 being an organic anionic polymer according to the
invention, preferably an organic anionic polymer that is
water-soluble, has a weight average molecular weight of at least
about 500,000. Usually, the weight average molecular weight is at
least about 1 million, suitably at least about 2 million and
preferably at least about 5 million. The upper limit is not
critical; it can be about 50 million, usually 30 million.
The polymer P2 being an organic anionic polymer can have a charge
density less than about 14 meq/g, suitably less than about 10
meq/g, preferably less than about 4 meq/g. Suitably, the charge
density is in the range of from about 1.0 to about 14.0, preferably
from about 2.0 to about 10.0 meq/g.
In one embodiment of the present invention the process for
producing paper further comprises adding a polymer P1 being a
cationic polymer to the suspension after all points of high
shear.
The optional polymer P1 according to the present invention is a
cationic polymer having a charge density of suitably at least 2.5
meq/g, preferably at least 3.0 meq/g. Suitably, the charge density
is in the range of from 2.5 to 10.0, preferably from 3.0 to 8.5
meq/g.
The polymer P1 can be selected from inorganic and organic cationic
polymers. Preferably, the polymer P1 is water-soluble. Examples of
suitable polymers P1 include polyaluminium compounds, e.g.
polyaluminium chlorides, polyaluminium sulphates, polyaluminium
compounds containing both chloride and sulphate ions, polyaluminium
silicate-sulphates, and mixtures thereof.
Further examples of suitable polymers P1 include cationic organic
polymers, e.g. cationic acrylamide-based polymers;
poly(diallyldialkyl ammonium halides), e.g. poly(diallyldimethyl
ammonium chloride); polyethylene imines; polyamidoamines;
polyamines; and vinylamine-based polymers. Examples of suitable
cationic organic polymers include polymers prepared by
polymerization of a water-soluble ethylenically unsaturated
cationic monomer or, preferably, a monomer mixture comprising one
or more water-soluble ethylenically unsaturated cationic monomers
and optionally one or more other water-soluble ethylenically
unsaturated monomers. Examples of suitable water-soluble
ethylenically unsaturated cationic monomers include diallyl-dialkyl
ammonium halides, e.g. diallyldimethyl ammonium chloride and
cationic monomers represented by the general structural formula
(II):
##STR00002## wherein R.sub.1 is H or CH.sub.3; R.sub.2 and R.sub.3
are each H or, preferably, a hydrocarbon group, suitably alkyl,
having from 1 to 3 carbon atoms, preferably 1 to 2 carbon atoms; A
is O or NH; B is an alkyl or alkylene group having from 2 to 8
carbon atoms, suitably from 2 to 4 carbon atoms, or a hydroxy
propylene group; R.sub.4 is H or, preferably, a hydrocarbon group,
suitably alkyl, having from 1 to 4 carbon atoms, preferably 1 to 2
carbon atoms, or a substituent containing an aromatic group,
suitably a phenyl or substituted phenyl group, which can be
attached to the nitrogen by means of an alkylene group usually
having from 1 to 3 carbon atoms, suitably 1 to 2 carbon atoms,
suitable R.sub.4 including a benzyl group
(--CH.sub.2--C.sub.6H.sub.5); and X.sup.- is an anionic counterion,
usually a halide like chloride.
Examples of suitable monomers represented by the general structural
formula (II) include quaternary monomers obtained by treating
dialkylaminoalkyl(meth)acrylates, e.g.
dimethyl-aminoethyl(meth)acrylate, diethylaminoethyl(meth)acrylate
and dimethylaminohydroxypropyl(meth)acrylate, and
dialkylaminoalkyl(meth)acrylamides, e.g.
dimethylaminoethyl(meth)acryl-amide,
diethylaminoethyl(meth)acrylamide,
dimethylaminopropyl(meth)acrylamide, and
diethyl-aminopropyl(meth)acrylamide, with methyl chloride or benzyl
chloride. Preferred cationic monomers of the general formula (II)
include dimethylaminoethyl acrylate methyl chloride quaternary
salt, dimethylaminoethyl methacrylate methyl chloride quaternary
salt, dimethyl-aminoethyl acrylate benzyl chloride quaternary salt
and dimethylaminoethyl methacrylate benzyl chloride quaternary
salt.
The monomer mixture can contain one or more water-soluble
ethylenically unsaturated non-ionic monomers. Examples of suitable
copolymerizable non-ionic monomers include acrylamide and
acrylamide-based monomers, e.g. methacrylamide,
N-alkyl(meth)acrylamides, e.g. N-methyl (meth)acrylamide,
N-ethyl(meth)acrylamide, N-n-propyl(meth)acrylamide, N-isopropyl
(meth)acrylamide, N-n-butyl(meth)acrylamide,
N-t-butyl(meth)acrylamide and N-isobutyl (meth)acrylamide;
N-alkoxyalkyl(meth)acrylamides, e.g.
N-n-butoxymethyl(meth)acrylamide, and
N-isobutoxymethyl(meth)acrylamide; N,N-dialkyl(meth)acrylamides,
e.g. N,N-dimethyl (meth)acrylamide; dialkylaminoalkyl(meth)
acrylamides; acrylate-based monomers like
dialkyl-aminoalkyl(meth)acrylates; and vinylamines. The monomer
mixture can also contain one or more water-soluble ethylenically
unsaturated anionic or potentially anionic monomers, preferably in
minor amounts. The term "potentially anionic monomer", as used
herein, is meant to include a monomer bearing a potentially
ionisable group which becomes anionic when included in a polymer on
application to the cellulosic suspension. Examples of suitable
copolymerizable anionic and potentially anionic monomers include
ethylenically unsaturated carboxylic acids and salts thereof, e.g.
(meth)acrylic acid and salts thereof, suitably
sodium(meth)acrylate, ethylenically unsaturated sulphonic acids and
salts thereof, e.g. 2-acrylamido-2-methylpropanesulphonate,
sulphoethyl-(meth)acrylate, vinylsulphonic acid and salts thereof,
styrenesulphonate, and paravinyl phenol (hydroxy styrene) and salts
thereof. Examples of preferred copolymerizable monomers include
acrylamide and methacrylamide, i.e. (meth)acrylamide, and examples
of preferred cationic organic polymers include cationic
acrylamide-based polymer, i.e. a cationic polymer prepared from a
monomer mixture comprising one or more of acrylamide and
acrylamide-based monomers
The polymer P1 in the form of a cationic organic polymer can have a
weight average molecular weight of at least 10,000, often at least
50,000. More often, it is at least 100,000 and usually at least
about 500,000, suitably at least about 1 million and preferably
above about 2 million. The upper limit is not critical; it can be
about 30 million, usually 20 million.
Examples of preferred drainage and retention aids according to the
invention include: (i) cationic polysaccharide being cationic
starch, and polymer P2 being anionic silica-based particles; (ii)
cationic polysaccharide being cationic starch, and polymer P2 being
water-soluble or water-dispersible anionic acrylamide-based
polymer; (iii) polymer P1 being cationic acrylamide-based polymer,
cationic polysaccharide being cationic starch, and polymer P2 being
anionic silica-based particles; (iv) polymer P1 being cationic
polyaluminium compound, cationic polysaccharide being cationic
starch, and polymer P2 being anionic silica-based particles; (v)
polymer P1 being cationic acrylamide-based polymer, cationic
polysaccharide being cationic starch, and polymer P2 being
water-soluble or water-dispersible anionic acryl-amide-based
polymer;
According to the present invention, the cationic polysaccharide,
polymer P2, and, optionally, polymer P1 are added to the aqueous
cellulosic suspension after it has passed through all stages of
high mechanical shear and prior to drainage. Examples of high shear
stages include pumping and cleaning stages. For instance, such
shearing stages are included when the cellulosic suspension is
passed through fan pumps, pressure screens and centri-screens.
Suitably, the last point of high shear occurs at a centri-screen
and, consequently, the cationic polysaccharide, polymer P2, and,
optionally, polymer P1, are suitably added subsequent to the
centri-screen. Preferably, after addition of the cationic
polysaccharide, polymer P2, and, optionally, polymer P1, the
cellulosic suspension is fed into the headbox which ejects the
suspension onto the forming wire for drainage.
It may be desirable to further include additional materials in the
process of the present invention. Preferably, these materials are
added to the cellulosic suspension before it is passed through the
last point of high shear. Examples of such additional materials
include water-soluble organic polymeric coagulants, e.g. cationic
polyamines, polyamideamines, polyethylene imines, dicyandiamide
condensation polymers and low molecular weight highly cationic
vinyl addition polymers; and inorganic coagulants, e.g. aluminium
compounds, e.g. alum and polyaluminium compounds.
The cationic polysaccharide, polymer P2, and, optionally, polymer
P1, can be separately added to the cellulosic suspension. In one
embodiment, the cationic polysaccharide is added to the cellulosic
suspension prior to adding polymer P2. In another embodiment, the
polymer P2 is added to the cellulosic suspension prior to adding
the cationic polysaccharide. Preferably, the cationic
polysaccharide is added to the cellulosic suspension prior to
adding polymer P2. If polymer P1 is used, it may be added to the
cellulosic suspension prior to, simultaneous with, or after the
cationic polysaccharide. Preferably polymer P1 is added to the
cellulosic suspension prior to, or simultaneous with, the cationic
polysaccharide. Polymer P1 may be added to the cellulosic
suspension prior to or after the polymer P2. Preferably, polymer P1
is added to the cellulosic suspension prior to the polymer P2.
The cationic polysaccharide, polymer P2, and, optionally, polymer
P1, according to the invention can be added to the cellulosic
suspension to be dewatered in amounts which can vary within wide
limits. Generally, the cationic polysaccharide, polymer P2, and,
optionally, polymer P1, are added in amounts that give better
drainage and retention than is obtained when not making the
addition.
The cationic polysaccharide is usually added in an amount of at
least about 0.001% by weight, often at least about 0.005% by
weight, calculated as dry polymer on dry cellulosic suspension, and
the upper limit is usually about 5.0, suitably about 2.0 and
preferably about 1.5% by weight.
Similarly, the polymer P2 is usually added in an amount of at least
about 0.001% by weight, often at least about 0.005% by weight,
calculated as dry polymer or dry SiO.sub.2 on dry cellulosic
suspension, and the upper limit is usually about 2.0 and suitably
about 1.5% by weight.
Likewise, the optional polymer P1 is, when used, usually added in
an amount of at least about 0.001% by weight, often at least about
0.005% by weight, calculated as dry polymer on dry cellulosic
suspension, and the upper limit is usually about 2.0 and suitably
about 1.5% by weight.
The process of this invention is applicable to all papermaking
processes and cellulosic suspensions, and it is particularly useful
in the manufacture of paper from a stock that has a high
conductivity. In such cases, the conductivity of the stock that is
dewatered on the wire is usually at least about 1.5 mS/cm,
preferably at least 3.5 mS/cm, and more preferably at least 5.0
mS/cm. Conductivity can be measured by standard equipment such as,
for example, a WTW LF 539 instrument supplied by Christian
Berner.
The present invention further encompasses papermaking processes
where white water is extensively recycled, or recirculated, i.e.
with a high degree of white water closure, for example where from 0
to 30 tons of fresh water are used per ton of dry paper produced,
usually less than 20, preferably less than 15, more preferably less
than 10 and notably less than 5 tons of fresh water per ton of
paper. Fresh water can be introduced in the process at any stage;
for example, fresh water can be mixed with cellulosic fibers in
order to form a cellulosic suspension, and fresh water can be mixed
with a thick cellulosic suspension to dilute it so as to form a
thin cellulosic suspension to which the cationic polysaccharide,
polymer P2, and, optionally, polymer P1, are added after all points
of high shear.
The process according to the invention is used for the production
of paper. The term "paper", as used herein, of course include not
only paper and the production thereof, but also other web-like
products, such as for example board and paperboard, and the
production thereof. The process can be used in the production of
paper from different types of suspensions of cellulosic fibers, and
the suspensions should preferably contain at least 25% and more
preferably at least 50% by weight of such fibers, based on dry
substance. The suspensions can be based on fibers from chemical
pulp, such as sulphate and sulphite pulp, thermo-mechanical pulp,
chemo-thermomechanical pulp, organosolv pulp, refiner pulp or
groundwood pulp from both hardwood and softwood, or fibers derived
from one year plants like elephant grass, bagasse, flax, straw,
etc., and can also be used for suspensions based on recycled
fibers. The invention is preferably applied to processes for making
paper from wood-containing suspensions.
The suspension also contain mineral fillers of conventional types,
such as, for example, kaolin, clay, titanium dioxide, gypsum, talc
and both natural and synthetic calcium carbonates, such as, for
example, chalk, ground marble, ground calcium carbonate, and
precipitated calcium carbonate. The stock can of course also
contain papermaking additives of conventional types, such as
wet-strength agents, sizing agents, such as those based on rosin,
ketene dimers, ketene multimers, alkenyl succinic anhydrides,
etc.
Preferably the invention is applied on paper machines producing
wood-containing paper and paper based on recycled fibers, such as
SC, LWC and different types of book and newsprint papers, and on
machines producing wood-free printing and writing papers, the term
wood-free meaning less than about 15% of wood-containing fibers.
Examples of preferred applications of the invention include the
production of paper and layer of multilayered paper from cellulosic
suspensions containing at least 50% by weight of mechanical and/or
recycled fibres. Preferably the invention is applied on paper
machines running at a speed of from 300 to 3000 m/min and more
preferably from 500 to 2500 m/min.
The invention is further illustrated in the following examples
which, however, are not intended to limit the same. Parts and %
relate to parts by weight and % by weight, respectively, unless
otherwise stated.
EXAMPLES
The following components were used in the examples: C-PAM
Representing polymer P1. Cationic acrylamide-based polymer prepared
by polymerisation of acrylamide (60 mole %) and
acryloxyethyltrimethyl ammonium chloride (40 mole %), the polymer
having a weight average molecular weight of about 3 million and
cationic charge of about 3.3 meq/g. C-PS 1: Cationic starch
modified with 2,3-hydroxypropyl trimethyl ammonium chloride to a
degree of cationic substitution (DS.sub.C) of 0.05 and having a
cationic charge density of about 0.3 meq/g. C-PS 2: Cationic starch
modified with 2,3-hydroxypropyl trimethyl ammonium chloride to a
degree of cationic substitution (DS.sub.C) of 0.11 and having a
cationic charge density of about 0.6 meq/g. Silica Representing
polymer P2. Anionic inorganic condensation polymer of silicic acid
in the form of colloidal aluminium-modified silica sol having an S
value of about 21 and containing silica-based particles with a
specific surface area of about 800 m.sup.2/g. A-PAM: Representing
polymer P2. Anionic acrylamide-based polymer prepared by
polymerisation of acrylamide (80 mole %) and acrylic acid (20 mole
%), the polymer having a weight average molecular weight of about
12 million and anionic charge density of about 2.6 meq/g. A-X-PAM:
Representing polymer P2. Anionic crosslinked acrylamide-based
polymer prepared by polymerisation of acrylamide (30 mole %) and
acrylic acid (70 mole %), the polymer having a weight average
molecular weight of about 100.000 and anionic charge density of
about 8.0 meq/g.
Example 1
Drainage performance was evaluated by means of a Dynamic Drainage
Analyser (DDA), available from Akribi, Sweden, which measures the
time for draining a set volume of stock through a wire when
removing a plug and applying vacuum to that side of the wire
opposite to the side on which the stock is present.
Retention performance was evaluated by means of a nephelometer,
available from Novasina, Switzerland, by measuring the turbidity of
the filtrate, the white water, obtained by draining the stock. The
turbidity was measured in NTU (Nephelometric Turbidity Units).
The stock used in the test was based on 75% TMP and 25% DIP fibre
material and bleach water from a newsprint mill. Stock consistency
was 0.76%. Conductivity of the stock was 1.5 mS/cm and the pH was
7.1.
In order to simulate additions after all points of high shear, the
stock was stirred in a baffled jar at different stirrer speeds.
Stirring and additions were made according to the following: (i)
stirring at 1000 rpm for 25 seconds, (ii) stirring at 2000 rpm for
10 seconds, (iii) stirring at 1000 rpm for 15 seconds while making
additions, and (iv) dewatering the stock while automatically
recording the dewatering time.
Additions to the stock were made as follows: The first addition
(addition levels of 5, 10 or 15 kg/t) was made 25 or 15 seconds
prior to dewatering and the second addition (addition levels of 5,
10 or 15 kg/t) was made 5 seconds prior to dewatering.
Table 1 shows the dewatering effect at different addition points.
The cationic starch addition levels were calculated as dry product
on dry stock system, and the silica-based particles were calculated
as SiO.sub.2 and based on dry stock system.
Test No. 1 shows the result without any additives. Test Nos. 2 to
6, 8, 10 to 14 and 16 illustrate processes used for comparison
(Ref.) and Test Nos. 7, 9, 15 and 17 illustrate processes according
to the invention.
TABLE-US-00001 TABLE 1 Addition Dewa- Addition Levels tering Tur-
Test First Second Time [s] [kg/t] Time bidity No. Addition Addition
1.sup.st./2.sup.nd 1.sup.st./2.sup.nd [s] [NTU] 1 -- -- -- -- 85.2
132 2 C-PS 1 Silica 25/-- 10/-- 73.2 62 3 C-PS 1 Silica 15/-- 10/--
54.8 61 4 C-PS 1 Silica 25/-- 15/-- 81.6 70 5 C-PS 1 Silica 15/--
15/-- 57.1 57 6 C-PS 1 Silica 25/5 10/0.5 54.5 53 7 C-PS 1 Silica
15/5 10/0.5 46.4 61 8 C-PS 1 Silica 25/5 15/0.5 49.9 59 9 C-PS 1
Silica 15/5 15/0.5 38.2 62 10 C-PS 2 Silica 25/-- 5/-- 57.5 66 11
C-PS 2 Silica 15/-- 5/-- 51.7 61 12 C-PS 2 Silica 25/-- 10/-- 48.7
59 13 C-PS 2 Silica 15/-- 10/-- 36.6 52 14 C-PS 2 Silica 25/5 5/0.5
52.9 61 15 C-PS 2 Silica 15/5 5/0.5 48.7 52 16 C-PS 2 Silica 25/5
10/0.5 28.3 43 17 C-PS 2 Silica 15/5 10/0.5 25.5 51
It is evident from Table 1 that the process according to the
present invention resulted in improved dewatering at the same time
the retention behaviour is about the same.
Example 2
Drainage performance and retention were evaluated according to
Example 1.
The stock used in the test was based on 75% TMP and 25% DIP fibre
material and bleach water from a newsprint mill. Stock consistency
was 0.78%. Conductivity of the stock was 1.4 mS/cm and the pH was
7.8.
In order to simulate additions after all points of high shear, the
stock was stirred in a baffled jar at different stirrer speeds.
Stirring and additions were made according to the following: (v)
stirring at 1500 rpm for 25 seconds, (vi) stirring at 2000 rpm for
10 seconds, (vii) stirring at 1500 rpm for 15 seconds, while making
additions according to the invention, and, (viii) dewatering the
stock while automatically recording the dewatering time.
Additions to the stock were made as follows: The first addition was
made 25 or 15 seconds prior to dewatering and the second addition
was made 5 seconds prior to dewatering. Additions to the stock were
made as follows: The first addition (addition levels of 5 or 10
kg/t) was made 25 or 15 seconds prior to dewatering and the second
addition (addition level of 0.1 kg/t) was made 5 seconds prior to
dewatering.
Table 4 shows the dewatering effect at different addition points.
The addition levels were calculated as dry product on dry stock
system.
Test No. 1 shows the result without any additives. Test Nos. 2, 3,
4 and 6 illustrate processes employing additives used for
comparison (Ref.) and Test Nos. 5 and 7 illustrate processes
according to the invention.
TABLE-US-00002 TABLE 2 Addition Dewa- Addition Levels tering Tur-
Test First Second Time [s] [kg/t] Time bidity No. Addition Addition
1.sup.st./2.sup.nd 1.sup.st./2.sup.nd [s] [NTU] 1 -- -- -- -- 85.3
138 2 C-PS 2 -- 25/-- 10/-- 51.9 74 3 C-PS 2 -- 15/-- 10/-- 43.2 72
4 C-PS 2 A-X-PAM 25/5 10/0.1 34.6 58 5 C-PS 2 A-X-PAM 15/5 10/0.1
33.3 55 6 C-PS 2 A-X-PAM 25/5 5/0.1 57.2 83 7 C-PS 2 A-X-PAM 15/5
5/0.1 48.7 72
It is evident from Table 2 that the process according to the
present invention resulted in improved dewatering and
retention.
Example 3
Drainage performance and retention were evaluated according to
Example 1.
The stock used in the test was based on 75% TMP and 25% DIP fibre
material and bleach water from a newsprint mill. Stock consistency
was 0.61%. Conductivity of the stock was 1.6 mS/cm and the pH was
7.6.
In order to simulate additions after all points of high shear, the
stock was stirred in a baffled jar at different stirrer speeds.
Stirring and additions were made according to the following: (ix)
stirring at 1500 rpm for 25 seconds, (x) stirring at 2000 rpm for
10 seconds, (xi) stirring at 1500 rpm for 15 seconds, while making
additions according to the invention, and, (xii) dewatering the
stock while automatically recording the dewatering time.
Additions to the stock were made as follows (addition levels in
kg/t): The optional polymer P1 was added 45 or 15 seconds prior to
dewatering, the cationic polysaccharide was added 25 or 10 seconds
prior to dewatering and the polymer P2 was added 5 seconds prior to
dewatering.
Additions to the stock were made as follows: The first addition
(addition level of 0.5 kg/t) was made 45 or 15 seconds prior to
dewatering, the second addition (addition levels of 5, 10 or 15
kg/t) was made 25 or 10 seconds prior to dewatering and the third
addition (addition level of 2 kg/t) was made 5 seconds prior to
dewatering.
Table 1 shows the dewatering effect at different addition points.
The addition levels were calculated as dry product on dry stock
system, and the silica-based particles were calculated as SiO.sub.2
and based on dry stock system.
Test No. 1 shows the result without any additives. Test Nos. 2 to
7, 9 to 11 and 13 to 15 illustrate processes used for comparison
(Ref.) and Test Nos. 8, 12 and 16 illustrate processes according to
the invention.
TABLE-US-00003 TABLE 3 Addition Addition Test First Second Third
Time [s] Levels [kg/t] Dewatering Turbidity No. Addition Addition
Addition 1.sup.st./2.sup.nd/3.sup.rd 1.sup.st./2.sup- .nd/3.sup.rd
Time [s] [NTU] 1 -- -- -- -- -- 54.1 134 2 C-PAM -- -- 15/--/--
0.5/--/-- 41.1 80 3 C-PAM -- Silica 45/--/5 0.5/--/2 49.4 94 4
C-PAM -- Silica 15/--/5 0.5/--/2 43.2 97 5 C-PAM C-PS 1 Silica
45/25/5 0.5/5/2 28.5 76 6 C-PAM C-PS 1 Silica 45/10/5 0.5/5/2 24.8
78 7 C-PAM C-PS 1 Silica 15/25/5 0.5/5/2 26.2 75 8 C-PAM C-PS 1
Silica 15/10/5 0.5/5/2 20.8 73 9 C-PAM C-PS 1 Silica 45/25/5
0.5/10/2 18.5 72 10 C-PAM C-PS 1 Silica 45/10/5 0.5/10/2 17.0 70 11
C-PAM C-PS 1 Silica 15/25/5 0.5/10/2 17.2 74 12 C-PAM C-PS 1 Silica
15/10/5 0.5/10/2 15.4 65 13 C-PAM C-PS 1 Silica 45/25/5 0.5/15/2
17.9 73 14 C-PAM C-PS 1 Silica 45/10/5 0.5/15/2 16.6 69 15 C-PAM
C-PS 1 Silica 15/25/5 0.5/15/2 15.3 73 16 C-PAM C-PS 1 Silica
15/10/5 0.5/15/2 15.1 63
It is evident from Table 3 that the process according to the
present invention resulted in improved dewatering and
retention.
Example 4
Drainage performance and retention were evaluated according to
Example 2. The same stock and stirring sequences were used as in
Example 2.
Additions to the stock were made as follows: The first addition
(addition level of 0.5 kg/t) was made 45 or 15 seconds prior to
dewatering, the second addition (addition level of 5 kg/t) was made
25 or 10 seconds prior to dewatering and the third addition
(addition level of 2 kg/t) was made 5 seconds prior to
dewatering.
Table 2 shows the dewatering effect at different addition points.
The addition levels were calculated as dry product on dry stock
system, and the silica-based particles were calculated as SiO.sub.2
and based on dry stock system.
Test No. 1 shows the result without any additives. Test Nos. 2 to 4
illustrate processes used for comparison (Ref.) and Test No. 5
illustrates the process according to the invention.
TABLE-US-00004 TABLE 4 Addition Addition Test First Second Third
Time [s] Levels [kg/t] Dewatering Turbidity No. Addition Addition
Addition 1.sup.st./2.sup.nd/3.sup.rd 1.sup.st./2.sup- .nd/3.sup.rd
Time [s] [NTU] 1 -- -- -- -- -- 54.1 134 2 C-PAM C-PS 2 Silica
45/25/5 0.5/5/2 14.9 75 3 C-PAM C-PS 2 Silica 45/10/5 0.5/5/2 14.5
66 4 C-PAM C-PS 2 Silica 15/25/5 0.5/5/2 17.3 73 5 C-PAM C-PS 2
Silica 15/10/5 0.5/5/2 13.5 64
It is evident from Table 4 that the process according to the
present invention resulted in improved dewatering and
retention.
Example 5
Drainage performance and retention were evaluated according to
Example 1. The same stirring sequences were used as in Example
2.
Additions to the stock were made as follows: The first polymer was
added 45 or 15 seconds prior to dewatering, the second polymer was
added 25 or 10 seconds prior to dewatering and the third polymer
was added 5 seconds prior to dewatering.
Additions to the stock were made as follows: The first addition
(addition level of 0.5 kg/t) was made 45 or 15 seconds prior to
dewatering, the second addition (addition level of 10 kg/t) was
made 25 or 10 seconds prior to dewatering and the third addition
(addition levels of 0.5+0.1 kg/t or 0.1 kg/t) was made 5 seconds
prior to dewatering.
The stock used in the test was based on 75% TMP and 25% DIP fibre
material and bleach water from a newsprint mill. Stock consistency
was 0.78%. Conductivity of the stock was 1.4 mS/cm and the pH was
7.8.
Table 3 shows the dewatering effect at different addition points.
The addition levels were calculated as dry product on dry stock
system, and the silica-based particles were calculated as SiO.sub.2
and based on dry stock system.
Test No. 1 shows the result without any additives. Test Nos. 2, 3,
4 and 6 to 8 illustrate processes used for comparison (Ref.) and
Test Nos. 5 and 9 illustrate processes according to the
invention.
TABLE-US-00005 TABLE 5 Addition Addition Test First Second Time [s]
Levels [kg/t] Dewatering Turbidity No. Addition Addition Third
Addition 1.sup.st./2.sup.nd/3.sup.rd 1.sup.st./2.sup.nd/3.sup.rd
Time [s] [NTU] 1 -- -- -- -- -- 85.3 138 2 C-PAM C-PS 2 Silica +
A-PAM 45/25/5 0.5/10/ 19.9 33 0.5 + 0.1 3 C-PAM C-PS 2 Silica +
A-PAM 45/10/5 0.5/10/ 18.5 37 0.5 + 0.1 4 C-PAM C-PS 2 Silica +
A-PAM 15/25/5 0.5/10/ 15.1 43 0.5 + 0.1 5 C-PAM C-PS 2 Silica +
A-PAM 15/10/5 0.5/10/ 13.6 38 0.5 + 0.1 6 C-PAM C-PS 2 A-X-PAM
45/25/5 0.5/10/0.1 30.6 49 7 C-PAM C-PS 2 A-X-PAM 45/10/5
0.5/10/0.1 24.8 46 8 C-PAM C-PS 2 A-X-PAM 15/25/5 0.5/10/0.1 25.6
56 9 C-PAM C-PS 2 A-X-PAM 15/10/5 0.5/10/0.1 22.6 43
It is evident from Table 5 that the process according to the
present invention resulted in improved dewatering at the same time
the retention behaviour is about the same.
* * * * *